Adjustable thermostat



March 27, C S, ADJUSTABLE THERMOSTAT Filed June 8, 1954 INSU TION- 25 lI I x INVENTOR. CHARLES S. MERTLER United States Patent O 2,740,o20ADJUSTABLE THERMOSTAT Charles S. Mertler, Masfield, Ohio, assignor toStevens Manufacturng Company, Inc., a corporation of Ohio ApplicationJune 8, 1954, Serial No. 435,179 16 Claims. (Cl. 200-139) The inventionrelates in general to adjustable thermostats and more particularly to animproved adjustng screw tor more consistent calibration of theadjustable positions of a thermostat.

Adjustable thermostats for controllable electrical devices have beenused for many years with the thermostat containing a bimetallic elementor other heat responsive means which controls the opening and closing ofelectrcal Contacts to control the application of electric energy to theelectrcal device, such as a household appliance. Such adjustablethermostats include some form of adjusting screw bearing upon or actingupon a movable contact carrying member, generally a resilient springoperated member. Such contact carrying member is quite frequently madeof Stainless steel to resist corrosion in the heated environment of thethermostat. The adjusting screw must act upon this stainless steelmember, and in most applications the adjusting screw .is threadablycarried in some manner by the base or frame of the thermostat andgenerally it must be electrically insulated from the contact carryingmember. This is for general safety purposes as well as fulfilling therequirements of the electrical appliance manufacturer.

For many years it has been customary to utilize a porcelain bar with agenerally pointed end carried by the adjusting screw and with thepointed end hearing against the Stainless steel contact carrying member.The Stainless steel member and pointed porcelain bar thus in the pasthave had high per unit area pressures at the point of mutual contactsince the contact carrying member is under rather high initial stress tomake sure that the contacts will open and close properly under alltemperature conditions. Stainless steel is a generally poor hearingmaterial and porcelain is generally abrasive and thus the high per unitarea pressure therebetween has frequently caused a chipping of the areaaround the point on the porcelain bar. This chipping causes very seriousabrasion once it occurs to thus further damage the stainless steelcontact carrying member and the porcelain bar.

ln practically all household electrical appliances the adjusting screwis calibrated for temperature and this chipping and/ or abrasion betweenthe Stainless steel member and porcelain bar seriously changes thepreset calibraton. When this occurs, the electrical appliance no longeroperates satsfactorily as far as the user is concerned; and therefore,the user becomes dissatisfied with the appliance. For this reasonelectrical appliance manufacturers are extremely desrous of obtainingthermostats which maintain their initial calibration throughout theuseful life of the thermostat.

It is accordingly an object of this invention to provide a thermostatmantaining uniform calibration throughout the life of the thermostat.

Another object of the invention is to provide a thermostat which resistswear and breakage on the Operating parts.

Another object of the invention is to provide a metal- 2 to-'metalhearing engagement between wearing parts of the thermostat.

Another object of the invention is to provide convex engaging surfaceson the wearing parts of a thermostat.

Still another object of the invention ,is to provide an adjusting screwwhich is insulated from a contact carrying member with the insulationprovided by a part of the adjusting screw and with this insulation notforming any part of the relatively rotatable portions of the thermostatwhich achieve the variations in adjustment positions.

Still another object of the invention is to provide an adjusting screwfor a thermostat wherein the error of calibration is lessened and isless dependent upon tolerance between fitted parts.

Other objects and a fuller Understanding of this invention may be had byreferr'ng to the following description and claims, taken in conjunctionwith the accompanying drawings, in which:

Figure 1 is a side elevational view of a thermostat embodying theinvention;

Figure 2 is a similar side view of the thermostat in a differentadjustment position;

Figure 3 is an enlarged sectional view through the adjusting screw ofthe thermostat; and

Figure 4 is a View similar to Fgure 3 but showing a prior art form ofthe device.

The Figures l, 2, and 3 show the improved form of adjusting screwutilized in the thermostat of the .invention. The thermostat isindicated generally by the reference numeral 11 and includes a base 12and a stack 13. The base 12 carries a nut 14 which has a neck portion 15passing through an aperture 16 in the base 12. T he lower end 17 of theneck 15 is swaged outwardly to fasten the nut 14 firmly onto the base12. A composite adjusting screw 20 threadably engages the nut 14. Theadjusting screw 20 cooperates with and moves a contact carrying member21. This contact carrying member 21 is carried in the stack 13 as is asecond contact carrying member 22 and a bimetallic strip 23. The members21 and 22 and strip 23 are mounted in the stack 13 by a headed hollowrivet 24 with insulating washers 25 insulating the parts 21, 22, and 23from each other and from the rivet 24. Terninal lugs 26 and 27 arerespectively in electrical contact with the contact carrying members 21and 22.

The bimetallic strip 23 carries a porcelain button 30 o that when thebimetallic strip 23 is moved upwardly by temperature changes as shown inFigure 2, the button 30 may contact and move the contact carrying member22. The contact carrying members 21 and 22 carry first and secondcontacts 31 and 32, respectively.

The thermostat 11 is representative of many forms of generally usedthermostats with which the adjusting screw 20 of this invention may beused. The Figure 3 shows to an enlarged scale the details ofConstruction of the adjusting screw 20. The screw 20 has male threads 35longitudinal bore n the tube 37. The tube 37 has lower and upper ends 39and 40, respectively, and both of these ends are preferably normal tothe aXis of the tube 37 which provides ease and cheapness ofmanufacture.

A steel pin 42 ,is carried in the lower end 39 of the tube 37. The pin42 has a shank 4-3 and a rounded head 44. The shank 43 may be cementedinto the bore 38 by cement 45 or alternatively the cement 45 may beeliminated if a sufiiciently close fit is provided between the shank 43and the bore 38. The head 44 has a flat underside 46 which abuts theflat face on the lower end 39 of the tube 37. This provides a relativelylarge and good hearing surface between the steel pin 42 and theporcelain tube 37. The head 44 of the pin is hardened, and in practicebecause of the small size, this means that the entire pin 42 ishardened.

An additional feature of the thermostat 11 may be provided; namely, atrim screw 49 for adjustment of the thermostat calibration in the field.The trim screw 49 is axially aligned with the screw 20 and extendsthrough a threaded aperture from the top of the screw 20 with the screw49 in engagement with the upper flat face 40 of the porcelain tube 37.The diameter of the screw 49 is greater than the diameter of the bore 38yet less than the diameter of the cavity 36, in order to permit movementof the screw 49 into the cavity 36.

operation The adjusting screw 20 is a principal feature of the inventionin that it eliminates the former problems of a rotatable porcelainmember hearing directly upon a contact carrying member. This prior artconstruction is shown in Figure 4 wherein a rotatable porcelain bar 52having a relatively sharp point 53 rotated and bore against a springcontact member 21A which would be similar to the member 21 in Figures lto 3. In this prior art construction of Fgure 4 high unit area pressureswere established at the point 53 and a hearing portion 54 on the springcontact member 21A. The Figure 1 shows the thermostat under adjustmentconditions indicating a high temperature setting, assuming that thebimetallc strip 23 moves upwardly with increasing temperature.

The Figure 2 shows the same thermostat adjusted for coni siderably lowertemperature conditions. A comparison of Figures l and 2 will show thatthe contact carrying member 21 initially must have a high degree of setin the upwardly directed position in order to maintain Satisfactorycontact pressure between the contacts 31 and 32 in. the high temperatureadjustment position shown in Figure 1. However, when the thermostat isadjusted for lower temperature conditions as in Figure 2, the adjustingscrew 20 must overcome a considerable amount of upward force asgenerated by the greatly deflected contact carrying member 21. This isshown enlarged in Figure 3. A similar position of the contact carryingmember ZIA is shown in Figure 4 and thus it will be realized that highper unit area pressures are encountered between the point 53 and thehearing portion 54.

In Figure 3 the rounded head 44 has a convex face 55 which provides agreatly enlarged hearing means for cooperation with a correspondingbearing portion 56 on the contact carrying member 21. Thus, it will beseen that the combination of the bearing means or rounded face 55 andthe hearing portion 56 establishes convex cooperating surfaces to thusprovide a greatly improved hearing condition between the adjusting screw20 and the mernber 21.

Still further, the rounded head 44 is hardened steel so that incooperation with the stainless steel contact carrying member 21 thereare two hard metals providing the hearing surface which is considerablysuperior to the porcelain bar 52 in contact with the member 21A as inFigure 4. In the prior art Construction in Figure 4 it was found thatfrequently a chip would break o the point 53 which would quickly abradethe hearing portion 54 to rapidly destroy the calibration of thethermostat. In Figure l a pointer 53 has been more or lessdiagrammatically indicated with the pointer cooperating with a dial orscale 59. This pointer and scale 58 and 59 are generally provided by theelectrical appliance manufacturer who incoporates the thermostat 11 intothe appliances manufactured. Such electrical appliance manufacturernaturally desires that the thermostat 11 maintain a constant calibrationthroughout its useful life, and any.

chipping and abrading of the sharp point 53 in Figure 4 would rapidlydestroy 'this calibration. The present'i'nvention of the steel pin 42.eliminates this problem and provides good hearing surfaces whichmaintain constant calibration of the adjusting screw or stud 20.

The flat faces 39 and 40 on the porcelain tube 37 make these tubes easyto manufacture and provide a good bearing surface both with theadjusting screw 20 and trim screw 49, if used, and the underside of thehead 44. Also, the outside diameter of the porcelain tube 37 may bemanufactured to a given diameter with close tolerances so that the tube37 fits closely within the cavity 36. This eliminates much of thesloppiness of fit formerly encountered which also tended to destroyaccurate calibration.

Although this invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of Construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:

l. An adjustment mechanism for a spring contact member insulativelycarried on the base of a thermostat, comprising, a male threaded studthreadedly carried by said base, bearing means cooperating with ahearing portion on said spring contact member, one of said hearing meansand said hearing portion having a conveX face, a body disposed betweensaid hearing means and said stud, and one of said stud, body, bearingmeans, and bearing portion being of insulating material to move saidcontact member relative to said base upon rotation of said stud.

2. An adjustment mechanism for a spring contact member insulativelycarried on the base of a thermostat, comprising, a male threaded studthreadedly carried by said base, hearing means cooperating with ahearing portion on said spring contact member, one of said bearing meansand said hearing portion having a conveX face, and insulating meanssupporting said hearing means from said stud to move said contact memberrelative to said base upon rotation of said stud.

3. An adjustment mechanism for a spring contact member insulativelycarried on the base of a thermostat, said mechanism comprising, a malethreaded stud threadedly carried by said base, a surface defining anaxial cavity in the lower end of said stud, a tube closely fittingwithin said cavity and having a lower end extending out of said cavity,a pin having a rounded head and a shank, said shank closely fitting inthe bore of said tube and said pin being carried in the lower end ofsaid tube with the underside of said head engaging the end of said tube,the rounded side of said head engaging said spring contact member uponrotation of said stud in said nut to move said contact member relativeto said base, and one of said head, shank, tube and stud being formed ofinsulating material to insulate said spring contact member fromsaidbase.

4. An adjustment mechanism for a spring contact member carried on thebase of a thermostat, said adjustment mechanism comprising, a malethreaded stud threadedly carried by said base, a surface defining anaxial cavity in the lower end of said stud, an insulated member fittingwithin said cavity and having a lower end extending out of said cavity,a hardened steel element having a rounded face, a part of said elementfitting in the bore of said insulated member, and said face engagingsaid spring contact member upon rotation of said stud in said facetomove said contact member relative to said base.

5. A thermostat comprising, a base, a spring` contact member carried onsaid base, a nut fixedly carried on said base, a male threaded studthreaded through said nut, a surface defining an axial cavity in thelower end of said stud, a porcelain body closely fitting within saidcavity and having a lower end extending out of said cavity, a secondcavity in said porcelain body, a metallic element disposed in saidsecondcavity, a rounded face on said metallic element engaging saidspring contact member' upon rotation of said stud in said nut to movesaid contact member relative to said base, a coaxial tapped hole in saidstud extending from the top end thereof to said axial cavity, thediameter of said tapped hole being less than that of said first axialcavity, and an adjustment screw threaded in said tapped hole and bearingagainst the top end of said porcelain body for axial adjustment thereofrelative to said stud.

6. A thermostat comprising, a base, a spring contact member carried onsaid base, a nut fixedly carried on said base, a male threaded studthreaded through said nut, a surface defining an axial cavity in thelower end of said stud, a porcelain body closely fitting within saidcavity and having a lower end extending out of said cavity, a secondcavity in said porcelain body, a metallc element disposed in said secondcavity, and a rounded face on said metallic element engaging said springcontact member upon rotation of said stud in said nut to move saidcontact member relative to said base.

7. A thermostat comprising, a base, a spring contact member carried onsaid base, a nut fixedly carried on said base, a male threaded studthreaded through said nut, a surface defining an axial cavity in thelower end of said stud, an insulated tube closely fitting within saidcavity and having a lower end extending out of said cavity, a hardenedsteel pin having a rounded head and a shank, said shank closely fittingin the bore of said tube and the underside on said head engaging the endof said tube, and said head engaging said spring contact member uponrotation of said stud in said nut to move said contact member relativeto said base.

8. A thermostat comprising, a base, a spring contact member carried onsaid base, a nut fixedly carried on said base, a male threaded studthreaded through said nut, a surface defining an axial cavity in thelower end of said stud, an electrically insulated tube closely fittingwithin said cavity and having a lower end extending out of said cavity,a hardened steel pin having a rounded head and a shank, said shankclosely fitting in the bore of said tube and said pin being cemented inthe lower end of said tube with the underside of said head engaging theend of said tube, and said head engaging said spring contact member uponrotation of said stud in said nut to move said contact member relativeto said base.

9. An adjusting screw for a thermostat and adapted for threadedconnection with the thermostat to provide ad justable movement of aspring contact member carried by said thermostat, said screw comprising,a surface defining an axial cavity in the lower end of said screw, aporcelain tube closely fitting within said cavity and having a lower endextending out of said cavity, a flat face on the lower end of said tubegenerally normal to the axis thereof, a hardened steel pin having a headand a shank, said shank closely fitting in the bore of said porcelaintube and said pin being cemented in the lower end of said tube with theunderside of said head engaging said flat face, said head engageablewith said spring contact member upon rotation of said screw in saidthermostat to move said contact member relative to said thermostat, andsaid head being rounded to thus maintain substantially constanttemperature calibration throughout the life ot' said thermostat.

10. A thermostat comprising, a base, a spring contact member carried onsaid base, a nut staked to said base, a male threaded stud threadedthrough said nut, a surface defining an axial cavity in the lower end ofsaid stud, a porcelain tube closely fitting within said cavity andhaving a lower end extending out of said cavity, a flat face on thelower end of said tube generally normal to the axis thereof, a hardenedsteel pin having a head and a shank, said shank closely fitting in thebore of said porcelain tube and said pin being cemented in the lower endof said tube with the underside of said head engaging said flat face,said head engaging said spring contact member upon rotation of said studin said nut to move said contact member relative to said base, and

said head beingrounded to thus maintain substantially constanttemperature calibration throughout the life of said thermostat.

11. An adjusting screw for a thermostat and adapted for threadedconnection with the thermostat to provide adjustable movement of aspring contact member carried by said thermostat, said screw comprising,a surface defining an axial cavity in the lower end of said screw, aporcelain tube closely fitting within said cavity and having a lower endextending out of said cavity, a flat face on the lower end of said tubegenerally normal to the axis thereof, a hardened steel pin having a headand a shank, said shank closely fitting in the bore of said porcelaintube and said pin being cemented in the lower end of said tube with theunderside of said head engaging said fiat face, said head engageablewith said spring contact member upon rotation of said screw in saidthermostat to move said contact member relative to said thermostat, saidhead being rounded to thus maintain substantially constant temperaturecalibration throughout the life of said thermostat, a coaxial tappedhole in said screw extending from the top end thereof to said axialcavity, the diameter of said tapped hole being less than that of saidaXial cavity and greater than that of said porcelain tube bore, and anadjustment screw threaded in said tapped hole and bearing against thetop end of said porcelain tube for axial adjustment thereof relative tosaid screw.

12. A thermostat comprising, a base, a spring contact member carried onsaid base, a nut staked to said base, a male threaded stud threadedthrough said nut, a surface defining an axial cavity in the lower end ofsaid stud, a porcelain tube closely fitting within said cavity andhaving a lower end extending out of said cavity, a flat face on thelower end of said tube generally normal to the axis thereof, a hardenedsteel pin having a head and a shank, said shank closely fitting in thebore of said porcelain tube and said pin being cemented in the lower endof said tube with the underside of said head engaging said fiat face,said head engaging said spring contact member upon rotation of said studin said nut to move said contact member relative to said base, said headbeing rounded to thus maintain substantially constant temperaturecalibration throughout the life of said thermostat, a coaxial tappedhole in said stud extending from the top end thereof to said axialcavity, the diameter of said tapped hole being less than that of saidaxial cavity and greater than that of said porcelain tube bore, and anadjustment screw threaded in said tapped hole and bearing against thetop end of said porcelain tube for axial adjustment thereof relative tosaid stud.

13. An adjustment mechansm for a movable member carried on the base of athermostat, comprising, a threaded stud threadedly carried by said base,a bearing portion on said movable member, bearing means on said stud andcooperating with said bearing portion, one of said bearing means andsaid bearing portion having a convex face, one of said stud, bearingmeans and bear ing portion being of insulating material, and saidcooperation between said bearing means and bearing portion providingmovement to said member relative to said base upon rotation of saidstud.

14. An adjustment mechansm for a movable member carried on the base of athermostat, comprising, an axially movable stud movably carried by saidbase, a bearing portion on said movable member, bearing means on saidstud, one of said bearing means and said bearing portion having a convexface, one of said stud, bearing means and bearing portion being ofinsulating material, and means for providing physical cooperationbetween said bearing means and bearing portion to move said mernberrelative to said base upon axial movement of said stud.

15. An adjustment mechansm for a spring member carried on the base of athermostat, comprising, an axial- &meme

ly movable stud movably carried' 'by said base, hearing means physicallycooperting With a beaing portion on said spring member, one of saidhearing meansvandr saii hearing portion having a convex face, andinsuiating means supporting said hearing means from said stud to movesaid contact member relative to said base upon axil movement of saidstud.

16. An adjustrnent mechanism for a movable member carried on the base ofa therrnostat, said adjustment mechanism comprising, an insulated memberhaving a 10 bore, a ha'rdened steel` element having a rounded face, apart of said element fitting in the bore of' said insulated member, saidfce being engageable With said' movable member, and means for providingaxiai movement of said insnlated member relative to said base to movesaid movabie member relative to said base.

References Cted in the file of this patent UNITED STATES PATENTS2,321,338 Ulanet June 8, 1943

